This invention relates to apparatus for sharpening the blades of a cylindrical rotor of a forage harvester, or the like, and without the necessity of removing the blades therefrom. The invention is an improvement over prior art sharpeners which are shown, for example, in U.S. Pat. No. 3,724,139, issued Apr. 3, 1973 to Leverenz and U.S. Pat. No. 3,863,403, issued Feb. 4, 1975 to Fleming, both of said patents assigned to an assignee common with the present invention.